Electrical discharge tube



g- 1933- c. J. R. H. VON WEDEL 1,923,521

ELECTRICAL TUBE Fi led Sept. 8, 1928 E v ML ame/wtoz 6/7/84 J hi 1?, ram/V1222 Patented Aug. 22, 1933 ELECTRICAL DISCHARGE TUBE Carl J. R. H. von Wedel, Berlin, Germany, as-

signor, by mesne assignments, to Electrons, Inc., a Corporation of Delaware Application September 8, 1928. Serial No. 304,697

5 Claims.

The present invention relates to the construction of electrical discharge tubes, and more particularly to a construction facilitating the removal of heat generated in such tubes to pre vent parts thereof from acquiring objectionally high temperatures.

An object is to provide for the removel of the excess quantities of heat common to the usual three electrode vacuum tubes of large powers employed for generating high frequency alterhating currents for electrical communication and like purposes, and particularly to avoid some of the difiiculties and disadvantages connected with the now generally practiced method of cooling such tubes with circulating water.

The invention will be readily understood by reference to the one figure of the drawing in following the description and explanation. V The figure illustrates a three electrode vacuum tube of the electron discharge type provided with features of the invention.

Referring to the figure the electrode structure of the tube is shown to include the usual electron emitting cathode E, which maybe of the indirectly heated type as indicated, or any other suitable form, a grid structure G, shown in the usual form of a supported spiral of wire surrounding the cathode, and a plate P shown as a cylinder closed at the upper end surrounding the cathode and grid arrangement. The cathode and grid are shown mounted on a glass stem S of arrangement usual to tube construction, the lead-in wires L forthese electrodes passing through the stem and sealed therein as well understood in practice. v

The plate P is shown mounted on a cup-shaped projection K from the stem S, the projection being preferably of glass sealed by an annular turnedwver weld at the lip B of the cup to on annular flange on the lower extremity of the cylinder plate P. The whole structure is enclosed in an envelope T of glass or other suitable material, which has a second stem S1 at the top portion through which a lead-in wire for a connection C to the plate P passes. This connection and leadin wire may be included in the lower end, but placed at the upper end a second function of support for the plate P is included, safe-guarding the sealing weld at the lip B.

A tubular connection K is shown associated with the stem S as a connection to a pump for evacuating the space within the plate P, and a similar connection K1 is shown associated with the stem S1 for evacuating and filling the space between the envelope T and plate P with a chosen gas.

In the operation of a discharge tube considerable heat is imparted to the anode or plate P by the impact energy of electrons and ions of the discharge as well as by radiation from the hot cathode, and if this heat is not removed at a sufficiently high rate the anodewill reach such high temperature as to vaporize its material or to cause it to soften and collapse. This heat generatingcondition becomes more and more severe as the potential between the anode and filament is increased for high power operation, so that so-called power transmitting tubes do not satisfactorily submit to the usual construction of tubes in which the anode is suspended in an almost completely evacuated space with little opportunity for disposing of the heat collected by it.

Heretofore solution of the problem of cooling power tubes has been sought in the practice of surrounding the anode with circulating cooling water, which has the practical disadvantage oi requiring a water supply and circulating system, and the electrical difficulty that the cathode is usually operated at the same potential as the water supply piping, that is ground potential, so that the difference of potential between the cathode and anode, usually many thousands of volts in a transmitting system, is applied across the anode and ground by way of the water of the cooling. system; Obviously this requires a high order of purity of the water in order to keep its conductivity low to prevent losses, by short-circuiting effects, so that practice has resorted to the use of carefully distilled water as the cooling medium; this in addition to the cor- .rosive effects of water in the presence of electrical potential differences which are diificult to isolate and control. v In the present invention I employ a fluid different from water as the cooling medium. Afterthe space between the anode P and envelope T is pumped fairly free from air I insert by cated by the series of corrugations R. The tube may be subjected to a stream of air, as from a blower, or immersed in'moving water or oil, to maintain a greater difference of temperature between the walls of the envelope T and the anode P to accelerate the convective action of the gas. 7

The needed gas-tight seal between the anode P and the stem S requires some consideration. After the lead-in wires are properly sealed into the stem any further heating of the stem will result in strains in the glass structure, and if the heating is of a high order these strains will result in breaking the gas-tight seal between the glass of the stem and the lead-in wires to.a degree suiiicient to permit air leakage into the tube to interfere with intended operation. This contingency is provided for by making the glass cup-shaped element K separate from the stem, so that the turned-over sealing weld at B can be made as between the anode P and the element as an operation without the presence of the stem S. After this weld is satisfactorily made the element K can be slipped over the stem S until contact is made with an annular shoulder of thestem at A, and a weld between the two elements then made by the local application of the necessary fusing heat in any suitable manner, this local application of fusing heat not carrying into the upper part of the stem to sufficient degree to sets up strains in the glass sufii-' cient-to break the seal of the lead-in wires.

In order to protect the gas-tight weld at B from the high temperature of the anode P extra large cooling corrugations or vanes, as indicated by M, may be arranged at the lower end of the structure. Copper and like soft metals have been found to be most satisfactory in making gas-tight welds with glass, but such metals are not the most suitable for anode materials in the matter of withstanding the high temperatures and disintegrating action of electron and ion bombardment. The requirements in this direction can be met by'imaking the lowerend only of the cylindrical anode of the desired softer metal, or by plating the lower end with copper or other soft metal to sufficient degree to get the desired effect for the weld with the glass at B. It is apparent that because the difference in pressure between the space inside the anode and the space outsidethe anode is not equal to atmospheric pressure, as is had in the usual construction of tubes, the diificulty of maintaining the gas-tight seal is decreased.

While I have described myinvention inparticular around a three electrode vacuum tube, no limitations are intended by the selection for mere illustrative purposes, the invention being one of broad application readily appreciated by those skilled in the art to which it relates,

Having fully described my invention, I claim: 1. An electron dischargetubecomprising in combination, a hollow metallic anode of relatively low mechanical strength and small heat radiating surface sealed to form an evacuated chamber therein, a cathode in said chamber, and a hollow outer vessel of relatively high mechanical strength and large radiating surface compared with said anode enclosing said anode and spaced and insulated therefrom, and a high velocity gaseous medium in said space, said medium being under pressure considerably below atmospheric pressure-and adapted to transfer heat mainly by convection from the anode to the outer vessel.-

2. A discharge tube comprising an envelope adapted to be evacuated, a plurality of substantially rigid supports carried by and within said envelope and spaced a fixed distance apart, a collapsible hollow anode fixed to one of said supports and suspended from the other support, anode forming with the former support a gas-tight space within the envelope adapted to be separately evacuated, and a cathode carried by the last-mentioned support within said space. 3. An electron discharge tube comprising in combination, an anode forming a wall of a vacuous chamber made in part of thin metal, deformable by atmospheric pressure, a cooperating electrode in said chamber, a gas tight envelope enclosing said anode, said envelope having a large radiating surface compared with said anode and adapted to resist atmospheric pressure, and a high velocity gas in the space between the anode and envelope under pressure considerably below atmospheric pressure and adapted to transfer heat from the anode to the outer envelope mainly by convection.

4. A discharge tube comprising an envelope capable of. resisting atmospheric pressure and having apair of oppositely disposed reentrantstems, a hollow anode suspended between said stems and forming with one of them a sealed" 5. The method for cooling the anode of a discharge tube in which the anode forms part of a wall defining an evacuated space and has insuificient mechanical strength to resist deformation by atmospheric pressure, which comprises the steps cf surrounding said anode with an envelope having an area several times larger than'the area of the anode and capable of resistin'g atmospheric pressure, and causing transfer of heat from the outer surface of said anode to the inner surface of said envelope mainly by gaseous convection in a high velocity gas at lowpressure relative to atmospheric pressure.

CARL J. R. voN WEDELr 

